Low application temperature hot melt adhesive

ABSTRACT

The invention relates to a low application temperature hot melt adhesive. More specifically, the low application temperature hot melt adhesive comprises olefin copolymers with an average Melt Index greater than 5 but less than about 35 g/10 minutes at 190° C. The adhesive is particularly useful in the construction of nonwoven articles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/188,167 filed Feb. 24, 2014, which is a divisionalapplication of U.S. patent application Ser. No. 13/400,218 filed Feb.20, 2012, which is a continuation of International Application No.PCT/US2010/045954 filed Aug. 19, 2010, which claims the benefit of U.S.Provisional Patent Application No. 61/235,551 filed Aug. 20, 2009, thecontents of all which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to hot melt adhesives. The adhesive isparticularly useful in the construction of nonwoven articles.

BACKGROUND OF THE INVENTION

Hot melt adhesives are applied to a substrate while in its molten stateand cooled to harden the adhesive layer. Such adhesives are widely usedfor various commercial and industrial applications such as productassembly and packaging, and have been widely used in the non-wovenindustry to make baby diapers and adult incontinence products. In theseapplications, adhesive is applied to at least one substrate such as, forexample, a film substrate (e.g., polyethylene), a non-woven substrate(e.g., polyolefin), or an elastic substrate (e.g., spandex) for bindingthe substrate to a second similar or different substrate.

Hot melt adhesives based on styrenic block copolymers have been usedcommercially as base polymers for hot melt adhesives and have foundwide-spread use in nonwoven construction applications, e.g., disposableabsorbent articles such as diapers, feminine hygiene articles, and adultincontinence devices. These products are typically applied attemperatures above 130° C. and often above 150° C. Lowering theapplication temperature of adhesives used in the manufacture of suchproducts below 120° C. would improve the thermal aging in applicationequipment and reduce issues with heat sensitive or lower basis weightsubstrates. However, in order to apply the adhesive below 120° C. usingcurrent application technology, the viscosity must be low enough tospray and extrude cleanly. To lower viscosity, lower molecular weightpolymers and higher levels of diluent have been used at the expense ofperformance of the hot melt adhesive. These approaches result in lowermechanical strength and more importantly less resistance to flow atelevated temperature. While the use of waxes to act as diluents as wellas crystalline reinforcing agents is known, this approach suffers from areduction in the effective open time the adhesive is capable of formingadequate bonds in the laminating processes used to make disposablearticles.

There is a continuing need for a hot melt adhesive that can be appliedat low temperature, i.e., below about 120° C., which has adequate opentime for bonding and has a high resistance to flow at elevatedtemperatures. Such attributes would make the adhesives particularlywell-suited for use in the manufacture of disposable articles. Theinvention is directed to this need.

BRIEF SUMMARY OF THE INVENTION

The invention provides a low application temperature hot melt adhesivecomprising an olefin copolymer, wherein the olefin copolymer has anaverage Melt Index greater than 5 but less than about 35 g/10 minutes at190° C. The olefin copolymer is a block copolymer and/or a randomcopolymer. The formulations of the low application temperature hot meltadhesive will also comprise a tackifier and a diluent. The formulationsof the low application temperature hot melt adhesive may furthercomprise a wax.

In another embodiment, the low application temperature hot melt adhesivecomprises an olefin copolymer, wherein the olefin copolymer have anaverage Melt Index greater than 5 but less than about 35 g/10 minutes at190° C., and at least one additional polymer selected from the groupconsisting of hydrogenated styrene block copolymers, amorphouspoly-α-olefins, and olefin copolymer with an average Melt Index ofgreater than about 35 g/10 minutes at 190° C. The formulations of thelow application temperature hot melt adhesive will also comprise atackifier and a diluent. The low application temperature hot meltadhesive may further comprise a wax.

In a further embodiment, the low application temperature hot meltadhesive comprises at least about 5 wt % of the olefin copolymer,wherein the olefin copolymers has an average Melt Index greater than 5but less than about 35 g/10 minutes at 190° C.; greater than zero but nomore than about 50 wt % of the additional polymer, wherein theadditional polymer is selected from the group consisting of hydrogenatedstyrene block copolymers, amorphous poly-α-olefins and olefin copolymerwith an average Melt Index of greater than about 35 g/10 minutes at 190°C.; from about 40 to about 70 wt % of a tackifier; from about 1 to about30 wt % of a diluent; from about 0.5 to about 5 wt % a wax; and from 0to about 5 wt % of an antioxidant.

Yet in another embodiment, the low application temperature hot meltadhesive comprises at least about 5 wt % of the olefin copolymer,wherein the olefin copolymer have an average Melt Index greater than 5but less than about 35 g/10 minutes at 190° C.; greater than zero but nomore than about 8 wt % of the additional polymer, wherein the additionalpolymer is a hydrogenated styrene block copolymer; from about 40 toabout 70 wt % of a tackifier; from 1 to about 30 wt % of a diluent; fromabout 0.5 to about 4 wt % a wax; and from 0 to about 5 wt % of anantioxidant.

In another embodiment, the adhesive of the invention comprises at leastabout 5 wt % of an olefin copolymer with an average Melt Index greaterthan 5 but less than about 35 g/10 minutes at 190° C.; greater than zerobut no more than about 50 wt % of an amorphous poly-α-olefin; from about40 to about 70 wt % of a tackifier; from 1 to about 30 wt % of adiluent; from about 0.5 to about 4 wt % a wax; and from 0 to about 5 wt% of an antioxidant.

In another embodiment, the adhesives of the invention comprises at least5 wt % of an olefin copolymer with an average Melt Index greater thanabout 5 but less than about 35 g/10 minutes at 190° C.; greater thanzero but no more than 50 wt % of an olefin copolymer with an averageMelt Index of greater than about 35 g/10 minutes at 190° C.; from 40 to70 wt % of a tackifier; from about 1 to 30 wt % of a diluent; from 0.5to 4 wt % a wax; and from 0 to 5 wt % of an antioxidant.

In a further embodiment, the formulated low application temperature hotmelt adhesive has a viscosity of below about 11,000 centipoises at 120°C.

Yet in another embodiment, the formulated low application temperaturehot melt adhesive has a yield stress (12 in/min extensional rate) ofmore than about 7 psi but less than about 50 psi at 25° C.

In another embodiment, the formulated low application temperature hotmelt adhesive has a cube flow of less than about 200% at 60° C.

In a further embodiment, the formulated low application temperature hotmelt adhesive has a cross-over temperature (when G″=G′) greater thanabout 70° C.

In another embodiment, the low application temperature hot melt adhesivecomprises an olefin copolymer with an average Melt Index greater than 5but less than about 35 g/10 minutes at 190° C.; and the adhesive has aviscosity of below about 11,000 centipoises at 120° C., a yield stress(12 in/min extensional rate) of more than about 7 psi but less thanabout 50 psi at 25° C., cube flow of less than about 200% at 60° C., anda cross-over temperature (when G″=G′) greater than about 70° C.

In a further embodiment, the low application temperature hot meltadhesive comprise (1) an olefin copolymer with an average Melt Indexgreater than 5 but less than about 35 g/10 minutes at 190° C., and (2)at least one additional polymer selected from the group consisting ofhydrogenated styrene block copolymers, amorphous poly-α-olefins, andolefin copolymer with an average Melt Index of greater than about 35g/10 minutes at 190° C.; and the adhesive has a viscosity of below about11,000 centipoises at 120° C., a yield stress (12 in/min extensionalrate) of more than about 7 psi but less than about 50 psi at 25° C.,cube flow of less than about 200% at 60° C., and a cross-overtemperature (when G″=G′) greater than about 70° C.

In a further embodiment, the low application temperature hot meltadhesive comprises (1) an olefin copolymer with an average Melt Indexgreater than 5 but less than about 35 g/10 minutes at 190° C., (2) atleast one additional polymer selected from the group consisting ofhydrogenated styrene block copolymers, amorphous poly-α-olefins, andolefin copolymer with an average Melt Index of greater than about 35g/10 minutes at 190° C., (3) about 40 to about 70 wt % of a tackifier,(4) from about 1 to about 30 wt % of a diluent (5) from about 0.5 toabout 4 wt % a wax and (6) from 0 to about 5 wt % of an antioxidant; andthe adhesive has a viscosity of below about 11,000 centipoises at 120°C., a yield stress (12 in/min extensional rate) of more than about 7 psibut less than about 50 psi at 25° C., cube flow of less than about 200%at 60° C., and a cross-over temperature (when G″=G′) greater than about70° C.

A further embodiment of the invention is directed to a process forbonding a substrate to a similar or dissimilar substrate using theadhesive. The process comprises applying to at least a portion of atleast a first substrate a molten hot melt adhesive, bringing a secondsubstrate in contact with the adhesive present on the first substrate,and allowing the adhesive to solidify, whereby the first substrate isbonded to the second substrate.

Another embodiment of the invention is directed to an articlemanufactured using the adhesives of the invention. The adhesives areparticularly advantageous when used in the construction of nonwovenabsorbent articles and garments, such as diapers and the like.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides the art with low application temperature hot meltadhesive that can be applied at temperatures below about 130° C.,preferable below about 120° C. The adhesive of the invention comprisesan olefin copolymer, wherein the olefin copolymer has an average MeltIndex range from above 5 to about 35 g/10 minutes at 190° C. The olefincopolymer of the adhesive comprises of a single olefin copolymer or amixture of olefin copolymers. The olefin copolymer is a block copolymerand/or a random copolymer. The low application temperature hot meltadhesive will also comprise a tackifier, a diluent, and a wax.

A necessary component of the adhesive is at least one olefin-basedcopolymer of ethylene and at least one C3 to C20 α-olefins. These olefincopolymers are produced by metallocene catalysis polymerization. Theolefin copolymer is a block copolymer and/or a random copolymer. Theolefin copolymer, herein, includes copolymers and terpolymers, whichalso may contain further monomers. The copolymers are any polymers thathave 2 monomers, and terpolymers are any polymers that have 3 monomers.Typical monomers are ethylene, propylene, butene and octene. Thesecopolymers are characterized by the fact that they have a narrowmolecular weight distribution. Such polymers are known in the literatureand are available from various manufacturer under the trade name Infuse(Dow Chemical), Engage (Dow Chemical), Versify (Dow Chemical), Vistamaxx(ExxonMobil), Exact (ExxonMobil), Tafmer (Mitsui Petrochemical) and LMPO(Idemitsu).

The olefin copolymers used in the low application temperature adhesivehave an average Melt Index range from above 5 to about 35 g/10 minutesat 190° C. An average melt index may be calculated by the followingformula:

${MI}_{AVG} = \frac{\sum\limits_{1}^{N}\lbrack {( {{wt}_{N}\mspace{14mu}\%\mspace{14mu} N} )( {MI}_{N} )} \rbrack}{\sum\limits_{1}^{N}\lbrack ( {{wt}_{N}\mspace{14mu}\%\mspace{14mu} N} ) \rbrack}$wherein, MI_(AVG) is the calculated average Melt Index, wt_(N) % of N isthe weight fraction of the N copolymer of the total adhesivecomposition, and MI_(N) is the of Melt Index value of the N copolymer.The Melt Index (interchangeably used also as Melt Flow Index) MI_(N)values are the rate of extrusion of molten polymer through a die ofspecified length and diameter at a specified temperature, according toASTM standard D-1238.

The low application temperature hot melt adhesive may further comprisean additional polymer. The additional polymer may be selected from thegroup consisting of hydrogenated styrene block copolymers, amorphouspoly-α-olefins, and olefin copolymer with an average Melt Index valuegreater than about 35 g/10 minutes at 190° C.

Exemplary A-B-A block copolymer such as styrene-butadiene andstyrene-isoprene, and exemplary A-B1-B2-A block copolymer (wherein B1and B2 may be the same or different monomer) such asstyrene-ethylene-butene or mixtures thereof may be used as theadditional polymer. Also included are the block or multi-blockcopolymers having the general configuration: A-B-A or A-B-A-B-A-B-wherein the polymer blocks A are non-elastomeric polymer blocks which,as homopolymers have glass transition temperatures above 20° C., whilethe elastomeric polymer blocks B are butadiene or isoprene or butadieneisoprene which is partially or substantially hydrogenated. Both linearand/or branched may be used in the practice of the invention. Typicalbranched structures contain an elastomeric portion with at least threebranches that can radiate out from a central hub or can be otherwisecoupled together.

The non-elastomeric blocks may comprise homopolymers or copolymers ofvinyl monomers such as vinyl arenes, vinyl pyridines, vinyl halides andvinyl carboxylates, as well as acrylic monomers such as acrylonitrile,methacrylonitrile, esters of acrylic acids, etc. Monovinyl aromatichydrocarbons include particularly those of the benzene series such asstyrene, vinyl toluene, vinyl xylene, ethyl vinyl benzene as well asdicyclic monovinyl compounds such as vinyl naphthalene and the like.Other non-elastomeric polymer blocks may be derived from □-olefins,alkylene oxides, acetals, urethanes, etc.

The hydrogenated styrene block copolymer is substantially saturatedmaterials having styrene end-blocks and ethylene-butylene,ethylene-propylene, butylene-butene or isobutylene mid-blocks and havinga di-block content of less than about 70%, a di-block content ofpreferably less than about 50% and more preferably less than about 30%.The styrene content is preferably from about 10% to about 40% by weightof the block copolymer, more preferably from about 10% to about 35% byweight and most preferably from about 10% to about 30% by weight of theblock copolymer. Preferred are styrene-ethylene-propylene-styrene blockcopolymers and styrene-ethylene-propylene-styrene block copolymers. Anon-limiting example of a styrene-ethylene-propylene-styrene blockcopolymers is Septon, available from Kuraray Company, Ltd, Japan. Anon-limiting example of a styrene-ethylene-butylene-styrene blockcopolymer is Kraton G-1650, available from Kraton. The midblocks arepreferably ethylene-butylene, ethylene-propylene or butylene-butene orisobutylene and are more preferably ethylene-butylene orethylene-propylene. The styrene content is preferably between about 10%and about 40% by weight of the block copolymer, more preferably fromabout 10% to about 35% by weight, even more preferably from about 10% toabout 30% by weight and most preferably from about 10% to about 25% byweight. The melt index of these block copolymers is preferably greaterthan about 5 g/10 min. and more preferably greater than about 10 g/10min. Useful examples include Kraton G-1652 available from Kraton, a 100%linear SEBS block copolymer having about 29% styrene and a melt index ofabout 10 g/10 min. These block copolymers are useful from greater than0% but up to about 8 wt % of the adhesive, preferably from about 1 wt %to about 6 wt % of the adhesive and more preferably from about 2 wt % toabout 5 wt % of the adhesive.

Amorphous poly-α-olefin is a polymer that can include random copolymersor terpolymers of ethylene, propylene, and butene, and othersubstantially amorphous or semi-crystalline propylene-ethylene polymers.Suitably, the amorphous poly-α-olefin (APAO) includes between about 20%and about 80% copolymers or terpolymers and between about 20% and about80% other substantially amorphous or semi-crystalline propylene-ethylenepolymers. Alternatively the APAO includes between about 30% and about70% copolymers or terpolymers and between about 30% and about 70% othersubstantially amorphous or semi-crystalline propylene-ethylene polymers.As yet another alternative, the APAO includes between about 40% andabout 60% copolymers or terpolymers and between about 40% and about 60%other substantially amorphous or semi-crystalline propylene-ethylenepolymers. APAO may be a 1-butene copolymer with ethylene or propylene,or a 1-butene terpolymer with ethylene and propylene, having anumber-average molecular weight of from about 5,000 to about 30,000,specifically about 10,000 to about 20,000. The butene-1 copolymer shouldinclude about 20% to about 65% by weight 1-butene, or about 30% to about55% by weight 1-butene, and a balance of the comonomer or monomer.Alternatively, the APAO may include an ethylene-propylene copolymerhaving up to 80% ethylene. An example of a commercially available APAOsuitable for use in the invention is Rextac (Rexene LLC), Eastoflex(Eastman Corpoartion) and Vestoplast (Evonik Corporation).

The olefin copolymer with an average Melt Index value greater than about35 g/10 minutes at 190° C. and mixtures thereof are ethylene and atleast one C3 to C20 α-olefins. These olefin copolymers are also producedby metallocene catalysis polymerization. The olefin copolymer is a blockcopolymer and/or a random copolymer. The olefin copolymer, herein,includes copolymers and terpolymers, which also may contain furthermonomers. Typical monomers are ethylene, propylene, butene and octene.

These copolymers characterized are by the fact that they have a narrowmolecular weight distribution. Such polymers are known in the literatureand are available from various manufacturers. One suitable olefinpolymer is AFFINITY from Dow Chemical.

The olefin copolymers have an average Melt Index range from above about35 g/10 minutes at 190° C. An average melt index may be determined bythe formula set above.

The adhesives of the invention will typically also comprise from about30 to about 70 wt % of a tackifying resin, preferably from about 40 toabout 70 wt %, more preferably from about 40 to about 65 wt % of atackifier which is compatible with the olefin copolymers and themidblock of the thermoplastic elastomer. Preferred are tackifiers havinga Ring and Ball softening point above about 25° C.

Suitable tackifiers include any compatible resins or mixtures thereofsuch as (1) natural or modified rosins such, for example, as gum rosin,wood rosin, tall oil rosin, distilled rosin, hydrogenated rosin,dimerized rosin, and polymerized rosin; (2) glycerol and pentaerythritolesters of natural or modified rosins, such, for example as the glycerolester of pale, wood rosin, the glycerol ester of hydrogenated rosin, theglycerol ester of polymerized rosin, the pentaerythritol ester ofhydrogenated rosin, and the phenolic-modified pentaerythritol ester ofrosin; (3) copolymers and terpolymers of natural terpenes, e.g.,styrene/terpene and □-methyl styrene/terpene; (4) polyterpene resinshaving a softening point, as determined by ASTM method E28,58T, of fromabout 80° to 150° C.; the latter polyterpene resins generally resultingfrom the polymerization of terpene hydrocarbons, such as the bicyclicmonoterpene known as pinene, in the presence of Friedel-Crafts catalystsat moderately low temperatures; also included are the hydrogenatedpolyterpene resins; (5) phenolic modified terpene resins andhydrogenated derivatives thereof, for example, as the resin productresulting from the condensation, in an acidic medium, of a bicyclicterpene and phenol; (6) aliphatic petroleum hydrocarbon resins having aBall and Ring softening point of from about 70° to 135° C.; the latterresins resulting from the polymerization of monomers consisting ofprimarily of olefins and diolefins; also included are the hydrogenatedaliphatic petroleum hydrocarbon resins; (7) alicyclic petroleumhydrocarbon resins and the hydrogenated derivatives thereof; and (8)aliphatic/aromatic or cycloaliphatic/aromatic copolymers and theirhydrogenated derivatives.

The desirability and selection of the particular tackifying agent candepend upon the specific types of olefin copolymer employed. Preferredtackifiers for use herein include polyterpenes, aliphatic resins,cycloaliphatic resins, aliphatic/aromatic, cycloaliphatic/aromatic, andnatural and modified rosin esters. More preferred are aliphatic resins,cycloaliphatic resins, polyterpenes, natural and modified rosin estersand mixtures thereof. Examples include Wingtack Extra from Sartomer,Piccotac from Eastman Chemical Company, Escorez from ExxonMobil ChemicalCompany, Sylvagum and Sylvalite from Arizona Chemical, and Piccolytefrom Ashland.

Diluent is defined, herein as an oil, plasticizer, liquid tackifier(having a Ring and Ball softening point below about 25° C.), syntheticliquid oligomer, and mixtures thereof. When present, the compositions ofthe invention will typically comprise the diluent in amounts of lessthan about 30 wt %. When the diluent is present, the adhesive willcomprise at least about 1 wt %, more typically at least about 5 wt % ofa diluent.

A non-limiting example of oils include paraffinic and naphthenicpetroleum oil, highly refined technical grade white petroleum mineraloils such as Kaydol oil from Crompton-Witco and naphthenic petroleum oilsuch as Calsol 5550 from Calumet Lubricants.

A non-limiting example of a plasticizer includes polar plasticizer,solid plasticizer, liquid plasticizer (natural and synthetic), andplasticizer that is primarily aliphatic in character and is compatiblewith the olefin copolymers and the thermoplastic elastomer midblock.Solid plasticizer is a solid at ambient temperature, and preferably hasa softening point above 60° C. Any solid plasticizer that is able tosubsequently recrystalize in the adhesive is suitable. Examples include1,4-cyclohexane dimethanol dibenzoate, Benzoflex 352, available fromGenovique Specialties. A non-limiting example of a natural liquidplasticizer is vegetable oil. Synthetic liquid plasticizers includeliquid polyolefins, iso-paraffins or paraffins of moderate to highmolecular weight. Examples include SpectraSyn Plus 6 from ExxonMobilChemical.

Exemplary liquid tackfiers (having a Ring and Ball softening point belowabout 25° C.) are liquid tackifying diluents that include polyterpenessuch as Wingtack 10 available from Sartomer, and Escorez 2520 availablefrom ExxonMobil Chemical.

The synthetic liquid oligomers are high viscosity oligomers ofpolybutene, polypropene, polyterpene, and etc. which are permanently inthe form of a fluid. Examples include polyisoprene, available as LIR 50from Kuraray, and Amoco's polybutenes available under the name Indopol.

Most preferred diluents are Wingtack 10 from Sartomer and syntheticliquid oligomer polybutenes such as Indopol 300 from Amoco.

The hot melt adhesive of the present invention may also comprise a wax.Petroleum based, conventional wax, natural-based wax, functionalizedwax, and polyolefin copolymers may be used in the practice of theinvention. The term petroleum derived wax includes both paraffin andmicrocrystalline waxes having melting points within the range of fromabout 130° F. to about 225° F. as well as synthetic waxes such a s lowmolecular weight polyethylene or Fisher-Tropsch waxes. Most preferredare polyethylene or Fisher-Tropsch waxes with a melting point of atleast about 175° F., more preferably at least about 195° F. and greater.Non-limiting examples include Paraffin 114 wax with melting point of205° F., available from Salsowax America, Inc. Amounts of polyethyleneor Fisher-Tropsch wax necessary to achieve the desired properties willtypically range from about 0.5 to about 10 wt % of a wax, preferablyless than 5 wt %, and more preferably less than 4 wt % of the totalcomposition.

The low temperature hot melt adhesive may optionally comprise additivessuch as antioxidants, stabilizers, pigments, and the like. Theseadditives may be added up to 5 wt % of the total composition.

An antioxidant or stabilizer may also be included in the adhesivecompositions described herein in amounts of up to about 3% by weight,more typically in amounts of about 0.5%. Among the stabilizers orantioxidants useful herein are the hindered phenols or hindered phenolsin combination with a secondary antioxidant such as distearylthiodipropionate (“DSTDP”) or dilauryl thio-dipropionate (“DLTDP”).Representative hindered phenols include: 1,3,5-trimethyl 2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; pentaerythrityltetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; pentaerythritoltetrakis (3-lauryl thiodipropionate);n-octadecyl-3,5-di-tert-butyl-4-hydroxyphenol)-propionate;4,4′-methylenebis (2,6-tert-butylphenol); 4,4′-thiobis(6-tert-butyl-o-cresol); 2,6-di-tertbutylphenol;6-(4-hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1,3,5-triazine;di-n-octadecyl 3,5-di-tert-butyl-4-hydroxy-benzyl-phosphonate;2-(n-octylthio)ethyl 3,5-di-tert-butyl-4-hydroxy-benzoate; and sorbitolhexa[3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate]. Preferred areIRGAFOS 168, a secondary antioxidant available from Ciba and IRGANOX1010, a hindered phenol primary antioxidant available from Ciba. Otherantioxidants include ETHANOX 330, a hindered phenol from Albermarle;SANTOVAR, a 2,5 ditert-amyl hydroquinone from Monsanto; and NAVAGARD P atris (p-nonylphenyl)phosphite from Uniroyal.

Other additives conventionally used in hot melt adhesives to satisfydifferent properties and meet specific application requirements also maybe added to the adhesive composition of this invention. Such additivesinclude, for example, fillers, pigments, flow modifiers, dyestuffs,which may be incorporated in minor or larger amounts into the adhesiveformulation, depending on the purpose.

In one embodiment, the low application temperature hot melt adhesive hasa viscosity of below about 11,000 cP at 120° C., yield stress (12 in/minextensional rate) of more than about 7 psi but less than about 50 psi at25° C., cube flow of less than about 200% at 60° C., and a cross-overtemperature (when G″=G′) greater than about 70° C.

In another embodiment, the low application temperature hot melt adhesivehas a viscosity of below about 9,500 centipoises at 120° C., a yieldstress (12 in/min extensional rate) range of from about 15 to about 45psi at 25° C., a cube flow of less than about 100% at 60° C., and across-over temperature (when G″=G′) greater than about 75° C.

Yet in another embodiment, the low application temperature hot meltadhesive has a viscosity of below about 8,500 centipoises at 120° C., ayield stress (12 in/min extensional rate) range of from about 16 toabout 40 psi at 25° C., a cube flow of about 0% at 60° C., and across-over temperature (when G″=G′) greater than about 80° C.

Melt viscosity is the resistance to shear in a molten state, quantifiedas the quotient of shear stress divided by shear rate at any point inthe flowing material. The melt viscosity for the low application hotmelt adhesive should be below about 11,000 cP at 120° C. to apply onto asubstrate.

Yield Stress is the stress beyond which yielding occurs for a polymer.This is defined as the yield point at which a material begins to deformplastically. Prior to the yield point, the material will deformelastically and will return to its original shape when the appliedstress is removed. Once the yield point is passed some fraction of thedeformation will be permanent and be non-reversible. This is a usefulguide to the limit to which a polymer may be stressed. An adhesive withyield stress (12 in/min extensional rate) value greater than about 7 psibut less than about 50 psi at 25° C. allows a good balance of providingcohesive strength to resist stress and unrecoverable deformation butsoft enough to maintain good adhesion with the flexible substrates.

Cube flow measures the resistance to flow. The stability of bondstrength of the adhesive on aging under distribution and storagetemperature is related to the resistance of the adhesive to flow in theinterface between substrates. Cube flow value indicates the cohesivestrength or adhesive modulus at elevated temperature. A low cube flowvalue correlates to adhesive's resistance to over-penetrate (bleed-out)into porous substrates over time.

The cross-over temperature is the temperature at which storage modulusG′ equals loss modulus G″. The modulus of elasticity (G′) is anindication of the stiffness of the adhesive and can be measured as isconventional in the art. Above the crossover temperature, loss modulusG″ will dominate and the adhesive will start to flow. The crossovertemperature in the semi-crystalline olefin adhesives correlates to themelting temperature of the crystalline domain and the strength of thecrystalline hard segment. A high cross-over temperature indicates ahigher melting point crystalline phase and a better overall cohesivestrength at elevated temperatures. A preferred cross-over temperature ofthe adhesive is greater than about 70° C., more preferably greater thanabout 75° C., and even more preferably greater than about 80° C.

Hot melt adhesives may be prepared using techniques known in the art.Typically, the adhesive compositions are prepared by blending thecomponents in the melt at a temperature of about 100° to 200° C. until ahomogeneous blend is obtained, generally about two hours. Variousmethods of blending are known and any method that produces a homogeneousblend is satisfactory.

The properties of the invention make it particularly useful in nonwovenapplications and, e.g., in bottle labeling or other applicationsinvolving plastic bonding or removable pressure sensitive adhesiveapplications.

The adhesive is applied to a substrate while in its molten state andcooled to harden the adhesive layer. The adhesive product can be appliedto a substrate such as a nonwoven article by a variety of methodsincluding coating or spraying in an amount sufficient to cause thearticle to adhere to another substrate such as tissue, nonwoven, or anunrelated material such as a low density polyolefin or otherconventionally employed substrates. In one embodiment of the invention,a disposable absorbent product is provided. The disposable absorbentproduct will typically comprises (1) a liquid-permeable topsheet, (2) aliquid-impermeable backsheet, which topsheet may be attached to thebacksheet, (3) an absorbent structure positioned between the topsheetand the backsheet, and (4) a hot melt adhesive having the propertiesdescribed herein.

The absorbent structure will typically comprise a nonwoven fabric. Anonwoven fabric is defined as an interlocking fiber networkcharacterized by flexibility, porosity and integrity. The individualfibers used to compose the nonwoven fabric may be synthetic, naturallyoccurring, or a combination of the two. The individual fibers may bemechanically, chemically or thermally bonded to each other.

Nonwovens are used commercially for a variety of applications includinginsulation, packaging (e.g., foods such as meat), household wipes,surgical drapes, medical dressings, and in disposable articles such asdiapers, adult incontinent products and sanitary napkins. Tissue is aclosely related material in which the individual fibers may or may notbe chemically bonded to one another.

The adhesives of the invention may be used to adhere the nonwoven ortissue to another substrate or component. The second substrate may beanother nonwoven, tissue, or an unrelated material such as, for example,polypropylene. The adhesive may be used to attach the topsheet to thebacksheet. Alternatively, the adhesive may be used to adhere either thetopsheet or the backsheet to other components of the disposableabsorbent product, such as tissue layers, leg flaps, fastening ears,tapes, or tabs, or other components typically used to construct adisposable absorbent product that are well known to one skilled in theart.

Those skilled in the art will recognize materials suitable for use asthe topsheet and backsheet.

Exemplary of materials suitable for use as the topsheet areliquid-permeable materials, such as spunbonded polypropylene orpolyethylene having a basis weight of from about 10 to about 25 gramsper square meter.

Backsheets often used in disposable absorbent products are generallyprepared from liquid-impermeable materials which function to containliquids, such as water, urine, menses, or blood, within the absorbentcore of the disposable absorbent product and to protect bedding and/or awears' outer garments from diluent or a plasticizer. Materials useful asa backsheet in a disposable absorbent product are generally impermeableto liquid but are permeable to vapor. Examples are liquid-imperviousmaterials such as polyolefin films, e.g., polypropylene andpolyethylene, as well as vapor-pervious materials, such as microporouspolyolefin films, sometimes referred to as breathable films.

A particularly desirable backsheet material is a film comprising apolyolefin polymer such as a linear low density polyethylene and afiller. As used herein a “filler” is meant to include particulates andother forms of materials which can be added to the film polymerextrusion blend and which will not chemically interfere with oradversely affect the extruded film but which are able to be uniformlydispersed throughout the film. When the film is stretched duringprocessing, the filler generally causes a network of holes to be formedin the film. Such holes are generally small enough to prevent thepassage of a liquid, but are generally large enough to allow vapor topass through the holes. Generally the fillers will be in particulateform and usually will have somewhat of a spherical shape with averageparticle sizes in the range of about 0.1 to about 7 microns. Bothorganic and inorganic fillers may be used in the practice of theinvention provided that they do not interfere with the film formationprocess. Examples of fillers include calcium carbonate (CaCO₃), variouskinds of clay, silica (SiO₂), alumina, barium sulfate, sodium carbonate,talc, magnesium sulfate, titanium dioxide, zeolites, aluminum sulfate,cellulose-type powders, diatomaceous earth, magnesium sulfate, magnesiumcarbonate, barium carbonate, kaolin, mica, carbon, calcium oxide,magnesium oxide, aluminum hydroxide, pulp powder, wood powder, cellulosederivatives, chitin and chitin derivatives.

EXAMPLES

Sample Preparation

Adhesive samples were formulated using techniques known in the art. Thecomponents to each adhesive samples are listed in the Tables 1-3. Anexemplary procedure involved placing approximately half of the totaltackifier in a jacketed mixing kettle, which is equipped with rotors,and raising the temperature to a range from about 100° C. to 200° C. Theprecise temperature utilized depends on the softening point of theparticular tackifier. When the tackifier has melted, stirring isinitiated and the rest of the components are added. Mixing and heatingare continued until a smooth homogeneous mass is obtained.

Components

Infuse 9817 is an olefin block copolymer having a density of 0.877 g/ccand a melt index of 15 g/10 min measured at 190° C., available from DowChemical.

Engage 8402 is an ethylene/l-octene copolymer having a density of 0.902g/cc and a melt index of 30 g/10 min measured at 190° C., available fromDow Chemical.

Engage 8200 is an ethylene/l-octene copolymer having a density of 0.870g/cc and a melt index of 5 g/10 min measured at 190° C., available fromDow Chemical.

Vistamaxx 6202 is a propylene/ethylene copolymer having a density of0.861 g/cc and a melt index of 7.4 g/10 min measured at 190° C.,available from ExxonMobil.

Kraton G 1650 is a selectively hydrogenated block copolymer havingterminal polymeric blocks of styrene and a mid-block of ethylene-butene(SEBS), available from Kraton.

Rextac RT 2732 is amorphous 1-butene-propene copolymer, available fromRexene LLC.

Affinity GA1900 is an ethylene/1-octene copolymer having a density of0.870 g/cc and a Brookfield viscosity of 8200 cps measured at 177° C.,available from Dow Chemical.

Escorez 5400 is a cycloaliphatic resin with softening points of 103° C.;available from Exxon Chemical.

Regalite 1090 is a hydrogenated hydrocarbon with softening point of 88°C.; available from Eastman Chemical.

Paraffin H4 wax is a synthetic Fischer-Tropsch wax with a melting pointof 96° C.; available from Sasolwax America, Inc.

Kaydol is a white mineral oil, available from Crompton-Witco.

Krystol 350 is a white mineral oil available from Petro Canada.

Calsol 5550 is a naphthenic oil, available from Calumet Lubricants.

Irganox 1010 is a hindered phenol antioxidant, available from CibaSpecialty Chemicals.

Eastotac H100 is a hydrogenated hydrocarbon resin available from EastmanChemical Company with a softening point of 100° C.

Komotac KT100B is polyterpene resin with a softening point of 100° C.,available from Guangdong KOMO Co.

Piccolyte C85 is polyterpene resin with a softening point of 85° C.,available from Ashland.

Piccolyte A115 is polyterpene resin with a softening point of 115° C.,available from Ashland.

Sylvagum TR90 is polyterpene resin with a softening point of 90° C.,available from Arizona Chemical.

Sylvalite RE 100 XL is a pentaerythritol ester of tall oil rosin,available from Arizona Chemical with a softening point of 100° C.

Adhesive Performance Characterization

1. Viscosity of the adhesive was measured using a standard Brookfieldviscometer, spindle 27, at 120° C.

2. Yield Stress was measured using a sample size of 0.125″ thick, 2.5″long dogbone shaped adhesive samples with 1″×1″ end tabs and a 0.5″×0.5″test area. The test area was extended on an Instron tester withpneumatic grips at a speed of 12 inches/min, and the results wererecorded.

3. Cube Flow at 60° C.: Molten adhesive was poured into a release moldto form a 1″ cube and allowed to condition at 25° C. for 24 hours. Thecube was removed from the mold and placed on standard graph paper (1 cmsquares or similar) and placed in a controlled oven at 130° F. for 24hours. The cube was then removed from the oven and the number of squarescovered by adhesive was recorded. The percent flow was calculated usingthe following equation.% flow=(Final Area−Initial Area)/Initial Area

4. Cross-over Temperature (G″=G′): A Rheometrics Dynamic MechanicalAnalyzer (Model RDA 700) was used to obtain the elastic (G′) modulus andthe loss (G″) modulus versus temperature. The instrument was controlledby Rhios software version 4.3.2. Parallel plates 8 mm in diameter andseparated by a gap of about 2 mm were used. The sample was loaded andthen cooled to about −100° C. and the time program started. The programtest increased the temperature at 5° C. intervals followed by a soaktime at each temperature of 10 seconds. The convection oven containingthe sample was flushed continuously with nitrogen. The frequency wasmaintained at 10 rad/s. The initial strain at the start of the test was0.05% (at the outer edge of the plates). An auto-strain option in thesoftware was used to maintain an accurately measurable torque throughoutthe test. The option was configured such that the maximum applied strainallowed by the software was 80%. The auto-strain program adjusted thestrain at each temperature increment if warranted using the followingprocedure. If the torque was below 200 g-cm the strain was increased by25% of the current value. If the torque was above 1200 g-cm it wasdecreased by 25% of the current value. At torques between 200 and 1200g-cm no change in strain was made at that temperature increment. Theshear storage or elastic modulus (G′) and the loss modulus (G″) werecalculated by the software from the torque and strain data.

Adhesives were prepared with the formulation shown in Table 1A and theperformance properties of the adhesives were tested as describe above.Results are shown in Table 1B.

TABLE 1A Adhesive Formulations Sample 1 (%) 2 (%) 3 (%) 4 (%) 5 (%) 6(%) 7 (%) 8 (%) A (%) Infuse 9817 13.5 10.0 12.0 5.0 13.0 5.0 Engage8402 15.0 10.0 7.0 5.0 Engage 8200 12.1 Vistamaxx 6202 9.0 Kraton G 16504.0 Rextac RT 2732 5.5 Affinity GA 1900 7.0 5.0 Escorez 5400 61.0 61.557.0 60.0 57.0 55.0 60.0 57.4 Regalite 1090 60.0 Paraffin H4 wax 3.0 3.01.5 3.0 3.0 3.0 3.0 Paraflint C80 2.0 Kaydol 22.0 21.0 Krystol 350 23.521.8 24.8 24.8 Calsol 5550 20.0 22.8 28.3 Irganox 1010 0.5 0.5 0.5 0.20.2 0.2 0.2 0.2 0.2

TABLE 1B Adhesive performance Sample 1 2 3 4 5 6 7 8 A Viscosity at 78757875 6560 4900 5400 7975 4200 10730 8375 120° C. (cP) Crossover Temp 8181 84 76 77 72 83 72 50 (° C.) Yield Stress (12′/ 40 40 16 50 27 19 1844 17 min extensional speed) (psi) Cube flow % (at 0 0 0 0 0 0 0 0 >200%60° C. for 24 hrs)

As shown above, the adhesive samples 1-8 made with olefin copolymer thathad an average melt index range above 5 and below 35, had a viscosity ofbelow about 11,000 centipoises at 120° C., a yield stress (12 in/minextensional rate) range of from about 7 to 50 psi at 25° C., a cube flowof less than about 200% at 60° C., and a cross-over temperature (whenG″=G′) greater than about 70° C. Sample A, where the olefin copolymerhad an average melt index of 5, fails to meet the same performance asshown in samples 1-8.

Adhesive Sample 3 was prepared with varying amounts of wax (as shown inTable 2). The performance properties (tested as describe above) of theadhesives with varying amounts of wax are shown in Table 2.

TABLE 2 Sample Adhesive Varying Wax Amounts Sample 3 9 10 11 B %Paraffin H4 wax 1.5 2.0 2.5 3.0 5.0 Viscosity at 120° C. 6560 7200 73507880 4900 (cP) Crossover Temp (° C.) 84 92 91 81 81 Yield Stress (psi)16 18 21 40 104 (12′/min extensional speed)

As shown in Table 2, adhesive samples that contain less than 5 wt % waxhad a viscosity of below about 11,000 centipoises at 120° C., a yieldstress (12 in/min extensional rate) range of from about 7 to 50 psi at25° C., a cube flow of less than about 200% at 60° C., and a cross-overtemperature (when G″=G′) greater than about 70° C.

Adhesive Samples 12-17 were prepared with various tackifiers. Theperformance properties (tested as describe above) of the adhesive withvarious tackifiers are shown in Table 3.

TABLE 3A Sample Adhesive With Various Tackifiers Sample 12 13 14 15 1617 Escorez 5400 54 Komotac KT100B 54 43.5 Piccolyte C85 61.5 PiccolyteA115 48 Sylvagum TR90 61.5 Sylvalite RE 100 XL 15 Viscosity at 7350 52627087 6125 7200 6200 120° C. (cP) Crossover Temp 91 90 92 89 83 81 (° C.)Yield Stress (psi) 21 19 23 21 24 28 (12′/min extensional speed)

As shown in Table 3, samples formulated with natural tackifiers such ascycloaliphatic resins, polyterpene resin and rosin ester tackifiersresulted in an adhesive with a viscosity of below about 11,000centipoises at 120° C., a yield stress (12 in/min extensional rate)range of from about 7 to 50 psi at 25° C., and a cross-over temperature(when G″=G′) greater than about 70° C.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

We claim:
 1. An adhesive composition consisting of: (a) at least greaterthan about 5 wt % of an ethylene monomer with at least one of C₃ to C₂₀α-olefin comonomer produced by metallocene catalysis polymerization,having an average Melt Index range of about 5 to about 35 g/10 minutesat 190° C. (b) an amorphous poly-α-olefin copolymer or a randomcopolymer having an average Melt Index range greater than about 35 g/10minutes at 190° C.; (c) a tackifier having a softening point of 115° C.or less (d) a diluent; and (e) optionally, wax, antioxidant, stabilizerpigment, or mixtures thereof.